1. Field of The Invention
The present invention relates to a circuit breaker for interrupting an electric circuit for a short time.
2. Description of The Related Art
In an electrical component system provided in a vehicle, when something is wrong with a load of a power window or the like, or when something is wrong with a wire harness or the like constituted by a plurality of electric wires connecting a battery and various loads to each other, a high-current fuse inserted between the battery and the wire harness is blown out to interrupt a connection between the battery and the wire harness, thereby preventing the loads, the wire harness and the like from being burnt and damaged.
However, in the case of the electric component system using such a high-current fuse, even if something is wrong with the load of the power window or the like, or something is wrong with the wire harness or the like connecting the battery and various loads, the fuse is not blown out unless a current equal to or greater than a tolerated value which is previously set for the high-current fuse. Therefore, various protecting apparatuses have been developed for detecting the current and interrupt the connection between the battery and the wire harness when a high current close to the tolerated value is continuously flowing.
FIG. 1 is a sectional view showing one example of the protecting apparatus using a bimetal (Japanese Utility Model Application Laid-open No. S64-29756). The protecting apparatus shown in FIG. 1 is made of insulation resin, and comprises a housing 103 formed at its upper portion with a fuse accommodating portion 102, a lid 113 for closing the fuse accommodating portion 102 such that the latter can be opened and closed, a power source terminal 105 disposed in a lower portion in the housing 103 such that an upper end of the power source terminal 105 projects into the fuse accommodating portion 102 and a lower end thereof is exposed outside, and the exposed portion of the power source terminal 105 being connected to a positive terminal of a battery 104, a load terminal 109 disposed in a lower portion in the housing 103 such that an upper end of the load terminal 109 projects into the fuse accommodating portion 102 and a lower end thereof is exposed outside, and the exposed portion of the load terminal 109 being connected to a load 108 through an electric wire 107 constituting a wire harness 106, a fusible member 110 made of low-melting metal disposed in the fuse accommodating portion 102, and having one end connected to an upper end of the power, source terminal 105 and the other end connected to an upper end of the load terminal 109, an intermediate terminal 111 disposed in a lower portion in the housing 103 such that the intermediate terminal 111 is located at an intermediate position between the power source terminal 105 and the load terminal 109 and a lower end of the intermediate terminal 111 is exposed outside, and the exposed portion being connected to a negative terminal of the battery 104, and a bimetal 112 which is made of a long plate-like member comprising two kinds of metal bonded together and which is disposed such as to be opposed to the fusible member 110 such that a lower end of the bimetal 112 is connected to an upper end of the intermediate terminal 111 and an upper end thereof being bent into an L-shape.
When an ignitor switch and the like of the vehicle are operated, and a current is flowing through a path comprising the positive terminal of the battery 104, the power source terminal 105, the fusible member 110, the load terminal 109, the electric wire 107 of the wire harness 106, the load 108, and the negative terminal of the battery 104, and when an abnormal condition occurs in the load 108 or in the wire harness 106 connecting the load 108 and a protecting apparatus 101, and a current equal to or greater than the tolerated value flows through the fusible member 110, the fusible member 110 is heated and blown out for protecting the load 108, the wire harness 106 and the like.
Further, even if something is wrong with the load 108 or the wire harness 106 connecting the load 108 and the protecting apparatus 101, and a large current flows through the fusible member 110, if the current does not exceed the tolerated value, the fusible member 110 is heated by the current flowing through the latter, and the bimetal 112 starts deforming. When a predetermined time is elapsed from the instant when the large current starts flowing through the fusible member 110, a tip end of the bimetal 112 comes into contact with the fusible member 110, and a large short-circuit current flows through the fusible member 110 in a path comprising the positive terminal of the battery 104, the power source terminal 105, the fusible member 110, the intermediate terminal 111, and the negative terminal of the battery 104, and the latter is blown out.
With the above structure, even when a current equal to or lower than the tolerated value flows for a preset time or longer, the circuit is interrupted to protect the wire harness 106 and the load 108.
As another protecting apparatus rather than this protecting apparatus 101, a protecting apparatus 121 shown in FIG. 2 has also developed (Japanese Utility Model Application Laid-open No. S64-29756).
The protecting apparatus 121 shown in FIG. 2 comprises a housing 122 made of insulation resin, a power source terminal 124 embedded in one side surface of the housing 122 and having a lower end connected to a positive terminal of a battery 123, and a load terminal 128 embedded in the other side surface of the housing 122 and having a lower end connected to a load 127 through an electric wire 126 constituting a wire harness 125. The protecting apparatus 121 further comprises an electric wire 131 including a fusible lead 129 which is made of low-melting metal and formed into U-shape and a heat-proof coating 130 formed such as to cover the fusible lead 129. The protecting apparatus 121 further comprises a coil 132. The coil 132 is made of shape-memory alloy which is formed into a shape wound around the electric wire 131 as shown in FIG. 2 when it is in a martensite phase state, and which is returned to its original phase shape fastening the electric wire 131 when it is heated to 120xc2x0 C. to 170xc2x0 C. The protecting apparatus 121 further comprises an external terminal 133 whose upper end is connected to one end of the coil 132 and whose lower end is connected to a negative terminal of the battery 123.
When an ignitor switch and the like of the vehicle are operated, and a current is flowing through a path comprising the positive terminal of the battery 123, the power source terminal 124, the fusible lead 129 of the electric wire 131, the load terminal 128, the electric wire 126 of the wire harness 125, the load 127 and the negative terminal of the battery 123, and when an abnormal condition occurs in the load 127 or in the wire harness 125 connecting the load 127 and a protecting apparatus 121, and a current equal to or greater than the tolerated value flows through the fusible lead 129, the fusible lead 129 is heated and blown out for protecting the load 127, the wire harness 125 and the like.
Further, even if something is wrong with the load 127 or the wire harness 125 connecting the load 127 and the protecting apparatus 121, and a large current flows through the fusible lead 129, if the current does not exceed the tolerated value, the fusible lead 129 is heated by the current flowing through the latter, and a temperature of the coil 132 rises. When a predetermined time is elapsed from the instant when the large current starts flowing through the fusible lead 129, and the temperature of the coil 132 rises to 120xc2x0 C. to 170xc2x0 C., the coil 132 changes from its martensite phase state to its original phase and bites into the heat-proof coating 130 which is softened by heat and comes into contact with the fusible lead 129, and a large short-circuit current flows through the fusible lead 129 in a path comprising the positive terminal of the battery 123, the power source terminal 124, the fusible lead 129, the coil 132, the external terminal 133, and the negative terminal of the battery 123, and the latter is blown out.
With the above structure, even when a current equal to or lower than the tolerated value flows for a preset time or longer, the circuit is interrupted to protect the wire harness 125 and the load 127.
FIG. 3 is a perspective view of a conventional fusible-link fusible conductor (Japanese Utility Model Application Laid-open No. S56-20254). This fusible-link fusible conductor 201 comprises a fusible conductor body 202 made of high-melting metal, and a fusible conductor piece 203 made of low-melting metal held on an intermediate portion of the fusible conductor body 202 through a pinching piece 202a, and a blowout characteristics are improved by dispersing low-melting metal and producing an alloy.
According to such a structure, if an excessive current flows through the fusible conductor body 202, the fusible conductor piece 203 is melted by heat caused by the excessive current, thereby blowing out the fusible conductor 201.
However, in the above-described conventional protecting apparatuses 101 and 121, there are problems as follows.
First, in the case of the protecting apparatus shown in FIG. 1, it is detected whether a large current flows through the fusible member 110 using the bimetal 112 made of two kinds of metals having different thermal expansion coefficients and bonded to each other. Therefore, if the magnitude of the current flowing through the fusible member 110, the bimetal 112 is deformed, and the time that elapsed before the circuit is interrupted is varied.
Thus, when a failure that a large current flows intermittently occurs, a temperature of the fusible member 110 does not rise more than a certain value, and there is an adverse possibility that the wire harness 106 or the load 108 may be burnt before the protecting apparatus 101 interrupts the circuit.
In the case of the protecting apparatus 121 shown in FIG. 2, it is detected whether a large current flows through the fusible lead 129 using the coil 132 made of shape-memory alloy. Therefore, if the magnitude of the current flowing through the fusible lead 129, the coil 132 is deformed, and the time that elapsed before the circuit is interrupted is varied.
Thus, when a failure that a large current flows intermittently occurs, a temperature of the fusible lead 129 does not raise more than a certain value, and there is an adverse possibility that the wire harness 125 or the load 127 may be heated excessively before the protecting apparatus 121 interrupts the circuit.
Further, in the protecting apparatuses shown in FIGS. 1 and 2, the heat reaction time of the bimetal 112 or the coil 132 which is a thermal-deformable electrical conduction member is varied depending upon the current flowing therethrough. Further, the heat reaction of the thermal-deformable electrical conduction member is not operated timely in some cases when an abnormal condition occurs (when excessive current flows).
In the case of the fusible conductor 201 shown in FIG. 3, the dispersion time of the low-melting metal is varied low-melting metal, it takes a long time for dispersing the low-melting metal and thus, the low-melting metal is not operated timely in some cases when an abnormal condition occurs (when excessive current flows).
Thereupon, as a circuit breaker which operates timely when an abnormal condition occurs (when excessive current flows), Japanese Patent Application No. H11-64055 (filed on Mar. 10, 1999) (not prior art) shows a circuit breaker. According to this circuit breaker, a pair of connecting terminals comprise a connecting terminal (e.g., buss bar) for a battery and a connecting terminal for a load. A conductor member (e.g., thermite case) is in contact with the pair of connecting terminals. When an abnormal condition of a vehicle occurs, the conductive member is moved upward by a compression spring or the like in response to an abnormal signal input from a control circuit or the like, thereby cutting off the electrical connection between the one connecting terminal and the other connecting terminal to interrupt the circuit.
However, this circuit breaker has problems that if a wire of the control circuit or the like may be broken, or if a current sensor or the like is damaged and the abnormal signal is not sent to the circuit breaker, the circuit can not be interrupted.
It is an object of the present invention to provide a circuit breaker capable of reliably interrupting a circuit in a short time to protect an electrical part when an abnormal signal of a vehicle is input, and capable of reliably interrupting the circuit even if the control circuit is out of order and the abnormal signal is not sent.
To achieve the above object, according to a first aspect of the present invention, there is provided a circuit breaker comprising: a first breaker including a first connecting terminal connected to a power source, a second connecting terminal connected to a load, and a conductive member coming into electrical contact with both the first and second connecting terminals, the first breaker moves the conductor member when a vehicle is under an abnormal condition to cut the electrical connection between the first and second connecting terminals, thereby interrupting a current; and a second breaker including a notch which is a fusible conductor formed on an intermediate portion of at least one of the first and second connecting terminals, the notch is blown out by heat caused by a current flowing through the at least one of the first and second connecting terminals, thereby interrupting the current, wherein a current is supplied from the power source to the load, and a circuit from the power source to the load is interrupted when the vehicle is under the abnormal condition.
According to the first aspect, the first breaker supplies a current to the load through the pair of connecting terminals comprising the first and second connecting terminals and the conductive member under a normal condition, and moves the conductive member based on the interrupting signal input when the vehicle is under the abnormal condition, thereby cutting off the electrical connection between the one connecting terminal and the other connecting terminal to interrupt the current. Therefore, it is possible to reliably interrupt the circuit within a short time.
Further, the second breaker includes the notch which is the fusible conductor formed on the intermediate portion of at least one of the first and second connecting terminals, and the notch is blown out by heat caused by the current flowing through the at least one of the first and second connecting terminals, thereby interrupting the current. That is, since the two kinds of circuit protecting members are provided, even when the interrupting signal is not input to the first breaker due to failure of a control unit or the like and the circuit can not be interrupted by the first breaker, the circuit can be interrupted by the second breaker, and an electrical part can be protected.
According to a second aspect of the invention, in the circuit breaker of the first aspect, the first breaker comprises a heating portion having the conductive member into which a heating agent is charged, an ignitor for igniting the heating agent by an interrupting signal, an outer case for accommodating the ignitor and the heating portion, an extensible resilient member, and a removable member for mounting the resilient member in its compressed state, the removable member being capable of being attached to and detached from the outer case, and being disposed in the vicinity or in contact with the heating portion when the removable member is mounted to the outer case, and the removable member is melted by heat caused by the heating agent.
According to the second aspect, the removable member for mounting the resilient member in its compressed state is disposed in the vicinity or in contact with the heating portion when the removable member is mounted to the outer case. When the ignitor ignited by the abnormal signal sent from outside, the heating agent charged into the heating portion is heated, and the removable member is melted by the heat. Since the resilient member which had been compressed is expanded to allow the heating portion to jump up, the electrical connection between the first and second connecting terminals is cut. Therefore, it is possible to reliably interrupt the circuit within a short time to protect the electrical part.
Further, since the removable member can be attached to and detached from the outer case, the attaching and detaching operation of the removable member is simple. Since the resilient member is held by the removable member, no external force is applied to the connected portion between the first and second connecting terminals and the heating portion.
According to a third aspect of the invention, in the circuit breaker of the second aspect, the second breaker comprises a low-melting metal as the fusible conductor.
According to the third aspect, since the low-melting metal is added as the fusible conductor, the low-melting metal is dispersed by the heat caused by the current flowing through the connecting terminal, the resistance is increased, thereby blowing out the fusible conductor to interrupt the circuit.
According to a fourth aspect of the invention, in the circuit breaker of the circuit breaker of the third aspect, the fusible conductor is mounted to the intermediate portion of at least one of the first and second connecting terminals by heat welding or caulking.
According to the fourth aspect, since the fusible conductor is mounted to the intermediate portion of at least one of the first and second connecting terminals by heat welding or caulking, the low-melting metal is dispersed by the heat caused by the current flowing through the connecting terminal, the resistance is increased, thereby blowing out the fusible conductor to interrupt the circuit.
According to a fifth aspect of the invention, in the circuit breaker of the third aspect, the interrupting signal is input to the first breaker when a value of the current became equal to or greater than a threshold value, and the value of the current when the fusible conductor is blown out is set greater than the threshold value.
According to the fifth aspect, since the interrupting signal is input to the first breaker when a value of the current became equal to or greater than a threshold value, and the value of the current when the fusible conductor is blown out is set greater than the threshold value, when the circuit can not be interrupted by the first breaker, the circuit can be interrupted by the second breaker, and the second breaker is not operated before the first breaker is operated.
According to a sixth aspect, in the circuit breaker of the second aspect, the heating portion is formed at its end with a side wall, the side wall and tip ends of the first and second connecting terminals are connected to each other by low-melting members.
According to the sixth aspect, since the side wall and tip ends of the first and second connecting terminals are connected to each other by low-melting members, if the removable member and the low-melting metal are melted by the heat of the heating agent, the heating portion jumps up to interrupt the electrical connection between the first and second connecting terminals. Therefore, it is possible to reliably interrupt the circuit within a short time to protect the electrical part. Further, since no spring force is applied to the low-melting metal which is the connected portion between the first and second connecting terminals and the heating portion, it is possible to enhance the reliability of the connected portion.